Blood Pressure Flashcards
How is blood pressure regulated in the short term?
Baroreceptor reflex
(Adjust sympathetic and parasympathetic input to the heart to alter CO, adjust sympathetic input to peripheral resistance vessels to alter TPR)
How is the blood pressure maintained over medium and longer time periods?
Complex interactions of neurohumeral responses
Directed at controlling sodium balance and thus extracellular fluid volume
How can controlling Na+ levels control plasma volume and ultimately blood pressure?
By changing the sodium levels you can change the extracellular fluid volume.
Plasma is part of the extracellular fluid compartment so technically controlling na+ you can control the plasma volume and plasma volume affects heart rate
What are the four pathways in which there is neurohumoral control over the circulation volume and hence BP?
- Renin-angiotensin-aldosterone system
- Sympathetic nervous system
- Antidiurectic hormone (ADH)
- Atrial natriuretic peptide (ANP)
What factors stimulate the release of renin from the kidneys?
A) reduced NaCl delivery to distal tube (the macula densa cells to be precise)
B) reduced perfusion pressure (fall in BP) in the kidney causes the release of renin (detected by baroreceptors in afferent arteriole)
C) sympathetic stimulation to juxtaglomerular apparatus increases release of renin
Where is renin released from?
Granular cells of juxtaglomerular apparatus in the kidneys (JGA)
These granular cells surround the afferent arteriole entering the glomerulus. They are located close to the distal tube which is surrounded by macula dense cells.
What are the two types of angiotensin II receptors?
AT1 - main actions via this one (gpcr)
AT2
What effect does angiotensin II have at the following sites:
- Arterioles
- Kidney
- Sympathetic NS
- Adrenal cortex
- Hypothalamus
- Vasoconstriction
- Stimulates Na+ reabsorption at the kidneys
- Increased release of Noradrenaline
- Stimulates release of aldosterone
- Increases thirst sensation (+ stimulates ADH release)
Where is aldosterone released from?
The adrenal cortex
What are the actions of aldosterone?
- stimulates Na+ and there water reabsorption
- activates apical Na+ channels (ENaC= epithelial Na channel) and apical K+ channel
- increases basolateral Na+ extrusion via Na/K/ATPase
What effect does aldosterone have on potassium?
It lower levels of K+
Where is ACE found?
Lungs predominantly (in epithelial cells)
What does ACE do? (2)
- It converts angiotensin I to angiotensin II
2. Converts bradykinin to peptide fragments
How does ACE’s action on bradykinin help to raise blood pressure?
Because bradykinin has vasodilator actions and breaking it down means there is less vasodilation
What is a side effect of ACE inhibitors and why does this happen?
Bad/dry cough
If ACE is inhibited then it doesn’t break down bradykinin
The accumulation of bradykinin causes the cough
Give an example of an ACE inhibitor
Captopril, lisinopril, perindopril, enalapril
In what way does the sympathetic NS raise blood pressure? (2)
Causes vasoconstriction of arterioles=increases BP (short term)
This vasoconstriction decrease the renal blood flow which stimulates Na+ retention which has a long term effect of raising your blood pressure
How is Na+ retained by stimulation of the sympathetic NS?
Activation of the apical Na/H-exchanger and basolateral Na/K/ATPase in PCT
The lack of blood flow also stimulates the renin release from juxtaglomerular cells leading to increased Ang II levels and aldosterone levels which further increased Na+ reabsorption
What is the main function of the ADH?
Formation of concentrated urine by retaining water to control plasma osmolarity
It increases water reabsorption in the distal nephrons
What is ADH stimulated by?
Plasma osmolarity or severe hypovolaemia
What system is in place to lower BP over the long term?
ANP (atrial Natriuretic peptides)
How do ANPs work?
Cause vasodilation of afferent arteriole
Increase blood flow to glomerulus
Inhibits Na+ reabsorption
Water retained
BP raised
What are prostaglandins?
Act as vasodilator locally
(PGE2) Enhance glomerular fitatrion and reduce Na+ reabsorption
Can have important protective function: Act as buffer to excessive vasoconstriction produced by SNS and RAA system
Important when levels of Ang II are high
What role does dopamine play in manning blood pressure?
Formed locally in the kidneys from circulating L-DOPA
Causes vasodilation and increases renal blood flow
Reduce reabsorption of NaCl (inhibits NaH exchanger and Na/K ATPase in principle cells of PCT and TAL)
What clinical use does dopamine have?
Used to treat Parkinson’s disease
Will lower BP so need to be aware of that!
Dopamine is not used as an antihypertensive
